The present invention relates to a change over switch for an on-load tap changer or change over switch for changing over taps of the transformer wiring or a the reactor wiring under loading or on-load state, more specifically, to a vacuum switch bulb type change over switch for an on-load tap changer, wherein vacuum bulbs or vacuum switch bulbs are used for current on-off contact points to be switched on and off for changing over the taps. In this system, three vacuum switch bulbs are used in a single resistor type for a single phase, and four vacuum switch bulbs are used in a double resistor type for a single phase, so that in a three phase switch, triple number of the vacuum switch bulbs is used.
FIG. 6 shows a structure of a conventional on-load tap changer (hereinafter sometimes referred to as "tap changer"), which uses a vacuum bulb type or vacuum switch bulb type change over switch. The tap changer is formed of a tap selector 210 disposed between a transformer wiring or a reactor wiring and a neutral point of a transformer, and a change over switch 207. The tap selector 210 further includes a tap selector drive mechanism 210A which performs a tap selection operation, and the change over switch 207 further includes a stored energy quick breaker 207A which changes over the taps of the change over switch 207.
The tap selector 210 and the change over switch 207 are vertically integrated together and hung in a transformer tank. The driving force is supplied to the stored energy quick breaker 207A and the tap selector drive mechanism 210A from a motor mounted in an electric actuator 201 via a speed reducer (not shown, a vertical drive shaft 202, a bevel gear 203, a horizontal drive shaft 204, a bevel gear 205, and an insulative drive shaft 206. The torque transferred to the insulative drive shaft 206 from the motor is transferred also to a tap selector drive shaft 210B coaxially aligned with the insulative drive shaft 206 via a crank 207D1 of the stored energy quick breaker 207A, which will be explained later. The on-load tap change over operation by the above described tap changer is performed as follows.
When a tap change over command is fed to an electric actuator 201, a motor mounted in the electric actuator 201 starts, and the torque of the motor is transferred to the insulative drive shaft 206 via a speed reducer (not shown), the vertical drive shaft 202, the bevel gear 203, the horizontal drive shaft 204, and the bevel gear 205. The torque transferred to the insulative drive shaft 206 is also transferred to the tap selector drive shaft 210B via the crank 207D1 rigidly coupled with the insulative drive shaft 206 to thereby transfer the driving force to the tap selector drive mechanism 210A, so that the tap selector 210 performs the tap selection operation.
At the same time, the crank 207D1 rigidly coupled with the insulative drive shaft 206 rotates around a rotation axis of the insulative drive shaft 206 and pulls a connector bar 207D2. As a result, an input plate 207D4 is rotated clockwise or counterclockwise direction around a rotation axis 207D3 to expand a tension spring 207D5 for energy storage. When the input plate 207D4 rotates beyond a predetermined angle, a clutch for preventing rotation of an output plate 207D6 comes off. Then, the output plate 207D6 rotates around its rotation axis 207D3, and the torque is transferred to a cam shaft 207B via an output shaft 207D7 and a clutch 207D8. Four cam plates 207Ba are mounted on the cam shaft 207B, and four cranks (not shown) connected to the respective cam plates 207Ba switch on or off corresponding vacuum switch bulbs 207E in a predetermined order, i.e. sequentially, by the drive spring to thereby complete the tap change operation. The sequential operation of the four vacuum switch bulbs 207E is shown in FIG. 7 together with the operation of the tap selector 210.
FIG. 7 illustrates operations of the tap selector 210 and the change over switch 207 for changing over from an operation using a tap T3 of a tap wiring St of a transformer or a reactor to an operation using a tap T4. When a tap change over command is fed to the electric actuator 201 (FIG. 6), the torque of the motor is transferred to the insulative drive shaft 206 and the torque is further transferred to the tap selector drive shaft 210B via the crank 207D1. Then, the tap selector 210 operates at first, and the tap at the even number side (FIG. 7) in the tap selector 210 is changed over from T2 to T4. This tap selection operation is performed by a Geneva mechanism, which is an intermittent motion mechanism installed on the tap selector drive mechanism 210A, and completed in an early stage of the rotation of the tap selector drive shaft 210B. Then, a change over operation of the change over switch 207, i.e. sequential operation of the four vacuum switch bulbs 207E, is awaited.
In the stored energy quick breaker 207A for driving the change over switch 207, since it takes time to store energy to the tension spring 207D5, as described above, the tap selection operation of the tap selector 210 has been completed at the time that the expansion of the tension spring for energy storage 207D5 reaches a predetermined value. In this condition, the change over operation from the tap T3 to the tap T4 is performed.
In this state, vacuum switch bulbs V1 and V3 on the side of the tap T3 are closed as shown in FIG. 7(A). The cam shaft 207B starts rotating when the expansion of the tension spring 207D5 reaches the predetermined value and the clutch for preventing rotation of the output plate 207D6 comes off. By the differences of shifting portions of the cam plates around the shaft changing from a convex portion to a concave portion or vice versa in the respective four cam plates 207Ba fixed to the cam shafts 207B, at first the vacuum switch bulb V1 is switched off as shown in FIG. 7(B), and a vacuum switch bulb V4 is switched on (FIG. 7(C)). Then, the vacuum switch bulb V3 is switched off, and finally a vacuum switch bulb V2 is switched on, by which the change over from the tap T3 to the tap T4 is completed. In FIG. 7, a symbol R designates a current limiting resistor. It takes a very short period of time for the vacuum switch bulbs to complete the sequential operation in the order of V1, V4, V3, V2 after the cam shaft 207B starts rotation, and the sequential operation is completed within 0.1 second.
In the change over switches for the on-load tap changer, the vacuum switch bulbs are used for the current on and off contact points, wherein the current switching is made in a vacuum condition, so that SF.sub.6 gas or insulator oil of the transformers or the reactors, in which the vacuum switch bulbs are immersed, is not deteriorated by the arc. Thus, many change over switches have been manufactured. Three vacuum switch bulbs are used in a single resistor type for a single phase, and four vacuum switch bulbs are used in a double resistor type for a single phase, so that nine or twelve vacuum switch bulbs are used in a three phase switch.
Conventionally, as shown in FIG. 6, the vacuum switch bulbs are mounted one by one in a casing 207C to constitute a change over switch, or a vacuum switch bulb is incorporated with its accessories into a unit and a plurality of the units is assembled to a change over switch. In a special case, for example, in order to solve the specific drawback occurring at the time of a change over operation, e.g. in a switch having a quick break mechanism, since the on-switching is performed by a strong spring of the quick break mechanism when the vacuum switch bulb is switched on, the contacts of the vacuum switch bulb chatter to cause quick wear of the contacts of the bulbs. Thus, as proposed in Japanese Patent Publication (KOKAI) 61-160918, a vacuum bulb for one phase and a space for means to solve the problem which occupies the same space with that of the vacuum switch bulb are united together in a single phase unit, and the means includes a function for driving its vacuum switch bulbs for one phase in a predetermined order.
The conventional change over switches, wherein the vacuum switch bulbs are installed one by one in a casing, or a plurality of units, each including a vacuum switch bulb and its accessories, is installed one by one in a casing, are complicated in the entire structure. Further, it requires tremendous manpower and time for taking out or installing the components and parts at the time of routine inspection or trouble shooting.
In view of the foregoing, an object of the present invention is to provide a vacuum switch bulb type three phase switch for an on-load tap changer, which is compact and requires little manpower and time for routine inspection and trouble shooting.